Well its a tough choice. Yes the ZX5 as stated by Col. The only other car I would mention is the academy. Yes its a shaft as well but never the less its pretty good. Cheap as well. Easy to maintain and in my opinion a better design than the ZX5.
http://www.modelrectifier.com/rc-pro...ars-trucks.asp
However if you can still find the rear belts, the spare layshaft gears, and a spur gear that fits (if you do not have screw on spur layshaft big problem) and bodyshell (Penkarc shells is no more but i know a few places that do zx shells or optima lwb mid shells that fit) then I see no reason why not the ZXR as its still rated as one of the best designed belt drive cars made. Still would compete easily with todays cars (I have proven this already) but the only problem is the spares and shells.
Down to you. Let us know your decision. any questions just ask.